Ozone decrease observed in the upper atmosphere following the May 11^th 2024 Mother’s day solar storm

Abstract. On May 11^th 2024, a succession of coronal mass ejections that merged together struck the Earth and induced large scale perturbations in the magnetosphere. During this event, satellite observations showed a large solar energetic proton (SEP) event associated to an extreme geomagnetic storm. At the same time, satellite observations of atmospheric ozone have been performed by AURA/MLS. In this work, we present the first observations of the effect of the storm of May and the following SEP of June 8^th on ozone concentration throughout the atmosphere. Observations of the MLS show that the event of May lead to stronger depletion of O₃ in the upper part of the atmosphere than in June. This difference is explained by the type of particle precipitation that occurred during the two events, with both protons and electrons in May and only protons in June. Neither event caused ozone depletion in the stratosphere while strong decreases are observed in the mesosphere. In May, mesospheric ozone depletion is observed during 18 days and reaches a maximum of 60 %. In addition, the storm of May also caused a noticeable decrease in ozone concentration (up to 20 %) at altitudes above 90 km.